Focal plane shutters



Dec. 17, 1963 H. J. c. NlEuwENHovEN ETAL 3,114,306

FOCAL PLANE SHUTTERS Filed March 31, 1959 Dec. 17, 1963 H. J. c.NlEuwENHovEN E'rAL 3,114,306

FOCAL PLANE SHUTTERS Filed March 3l. 1959 3 Sheets-Sheet 3 /f/ l1 7e 7/73 /a/ I l g /00 I 99 j D 0 D T 0 D 0 w 96 O i fas 93 31.. o 70 |106 9595 las as im I y@lf 97 5a United States Patent() 3,114,306 FOCAL PLANESHUTTERS Hendricus Jacobus Cornelis Nieuwenhoven, Rijswijk, and AlbertBouwers, The Hague, Netherlands, assignors to NN'. Optische lndustrie DeGuide Delft, Delft, Netherlands, a corporation of the Netherlands FiledMar. 31, 1959, Ser. No. 803,167 Claims priority, application Netherlands(ict. 30, 1958 4 Claims. (Qi. 95--12.5)

The invention relates generally to photography and, more particularly,to `an improved focal plane shutter for use in photographic cameras.

lIt is well-known in the art of photography that for establishingextremely short exposure times in the order of, for example, 2%00 of asecond or less, use must be made of focal plane shutters as it isgenerally impossible to accelerate the moving parts of between-the-lensshutters rapidly enough to completely'expose the lens aperture in asmall fraction of the exposure times.

It has recently been proposed to use in 4a between-thelens shutter anumber of constantly rotating blades instead of the conventionalintermittently moving blades which have definite rest positions and mustbe accelerated and stopped for each exposure. If high exposure speedsare to be obtained with this type of shutter the blades thereof must begiven a relatively high rotational speed and means must be provided toprevent the shutter blades from exposing the lens aperture at eachrevolution. To this end a rotating disc having a circular aperture ismounted adjacent the elements in the path of the light rays such that anexposure may be made only once per revolution of the disc. Though this-type of shutter is capable of somewhat higher exposure speeds than theconventional between-the-lens shutters it is relatively complicated instructure and does not afford a readily acceptable solution for smallcameras and, for example, c

cameras having interchangeable lenses. Furthermore, it is not readilypossible by means of this type of shutter to reduce the exposure time tovalues substantially below V1000 of a second.

Heretofore focal plane shutters have usually been made in 4the form of a`flexible cur-tain having a slit, which curtain is longitudinally guidedalong the focal plane and capable of being rolled up to effect anexposure.V lt has not been possible to reduce exposure time to valuesfar lower than 1/1000 of a second with the curtain type shutter withoutapplying excessive tension to the curtain and causing serious vibrationsof -the camera. y

It is a principal object of this invention to provide a focal planeshutter of rigid and relatively simple construction permitting extremelyshort exposure times, in

a range of exposure times where each exposure is below Y 1/1000 of asecond, to be obtained.

Another object of the invention is to provide a focal plane shuttercapable of working at high exposure repetition frequencies in additionto short exposure times.

Still another object of the invention is to provide an improved focalplane shutter for use in a stereo-photog-raphic camera.

Yet another object is in the provision, in a photographic camera, of animproved` focal plane shutter and film driving assembly whereby entirelynew results in the field of aerial photography may be obtained. Y

A feature of the focal plane shutter according to the invention is thatit is provided with a set of two, coaxial circular discs mountedIadjacent to and forward of the focal plane. The discs are rotatableabout an axis perpendicular to and intersecting the focal plane at apoint outside the effective image area. Each disc has a peripheralaperture extending radially inwardly. One of the apertures serves as anexposure aperture as it passes be- ICC fore the image area and its widthincreases linearly as it extends towards the periphery of the disc. Thediscs are rotatably driven at different speeds so related that thesecond aperture, during a certain time that the exposure aperture passesbefore the image area, allows light rays to pass on the focal `planewhereas during a number of revolutions of the exposure aperture beforeand after this time the light rays are prevented from entering by thedisc having Ithe second aperture.

Other objects, features Iand advantages of the invention will beunderstood from the following description and claims in conjunction withthe accompanying drawings which illustrate by way of example someembodiments of the focal plane shutter and associated mechanisms, and inwhich:

FIG. l is an elevation view of the focal plane shutter discs accordingto the present invention viewed from the focal plane,

FIG. 2 is a schematic sectional elevation View of an aerial cameraequipped with a focal plane shutter according to `the invention,

FIG. 3 is a schematic plan view partly sectional taken along linelll-III of FIG. 2,

FIG. 4 is a perspective view of a stereo-photographic camera equippedwith a focal plane shutter according 4to the invention, the cover of thecamera body and some other parts being omitted to show the interiorparts of the camera,

FlG. 5 is a perspective view similar to that of FIG. 4, part of thecamera cover being removed to show one of the film loops,

FiG. 6 is an elevation view similar to FIG. l and is illustrative of afocal plane shutter of a twin camera,

FIG. 7 is a perspective View of a driving mechanism for a twin cameraalternative to the driving mechanism shown in FIG. 4,

FIG. 8 is a cross-sectional view, taken along line VlIl-VIII of FIG. 9,of a miniature camera having a spring-driven focal plane shutteraccording to the invention,

FIG. 9 is a sectional view, taken along line IX--IX of FIG. 8, of theminiature camera shown in FIG. 9,

FIG. 10 is a focal plane shutter arrangement alternative to theembodiment shown in FIG. 1 and having three rotating discs. n

According to the drawings, in which similar parts have the samereference numeral, a disc 1 in FIG. l having a diameter of forexample,186` mm. has a sector-shaped, peripheral exposure aperture 2 extendingradially yinwardly yand of such radial length that a gate defining animage area 3, may be exposed thereby. The aperture is bounded by anangle of 3. Hence, when thedisc 1 is rotated at a speed of, for example,10,000 revolutions/minute about an axis S an exposure time of p. sec. isobtained. An exposure time of 1/1000 of a second requires a speed ofonly 500 revolutions per minute. Thus, it is apparent that exposuretimes in the range of from about 1000 microseconds down to about 50microseconds or even lower are obtainable with this arrangement, asconstant rotating speeds up to 10,000 rev/min. may be established verywell in practice.

In order to prevent the film from being exposed at each revolution ofdisc 1 a second disc 4 is provided axially spaced from disc 1 anddisposed in front of it. Disc 4 is rotatable about the same axis as Ithedisc 1 and is driven at a different speed which may be higher or lowerthan that of disc 1. In disc 4 a sector-shaped aperture 5 is providedand is bounded by an angle or arc which is larger than that of sector 2in disc 1. `If i-t is assumed that disc 1 is rotated at 9000revolutions/minute and disc 4 at 8100 revolutions/minute it is clearthat once in l0 revolutions of disc 1 the sector 2. is incorrespondatrasos ence with -the sector 5 in disc 4.' lf the discs l and4 have been well adjusted this correspondence will occur during the timethe exposure aperture 2 is in correspondence or alignment with the imagearea and, accordingly, an exposure is made. ln the case described theaperture 5 in disc l must cover an angle of about l2 in order to makesure that the aperture 2, which determines the exposure time, is freeduring the complete exposure time, whereas at the next revolutionaperture 2 is completely covered again by the disc d.

`In FIGS. 2 and 3 a camera lens hood 7 carries a lens system 7. Thislens hood is attached to a camera body 8, in which iilm spools 9 and liland the driving mechanism for ythe film and the shutter discs ll and 4iare housed. The camera shown is an aerial camera of a type adapted totake a series of rapid successive exposures taken at high aeroplanespeeds and a low fiying altitude.

`In cameras of this type two serious diiiiculties are encountered,namely, to prevent blurring of the image by the high image motion speedand to provide a high enough exposure repetition frequency necessary forobtaining overlapping pictures of the strip to be photographed. ln thecamera illustrated in FIGS. 2 and 3 these ditculties are overcome in asimple and reliable manner by applying a high speed focal plane shutterconstructed in accordance with the invention and by advancing the filmduring the series of exposures through the image area at a substantiallyconstant speed which is, preferably, somewhat higher than the speed ofthe image caused by the aeroplane speed. The film is advanced in thesame direction as the movement of the image. Then, image motion landfilm speed will largely compensate each other and the blurring asdetermined by the extremely short exposure time will be minor.

If it is assumed that, with the shutter data mentioned above, the filmis driven at a speed of 90 cm./sec. the successive exposures on the filmwill be separated by unexposed strips of 4 mm. If, furthermore, theplane is flying at an altitude of, for example, l5()` feet and a speedof about 300 rn./sec. and the camera objective has a focal length of tencentimeters then the image will be moving through the focal plane at aspeed of about sixty cm./sec. As the exposure time is about 5 Omicroseconds the resultant blurring is in the order of which is quitetolerable for the type of work involved. The successive pictures showterrain portions which overlap each other sufiiciently.

Returning to FIGS. 2 and 3, the disc l is pivotally mounted closeadjacent to the focal plane on a hollow shaft 11. Within this shaftthere is provided a spindle 12 for disc 4. The driving mechanism isshown Schematical'ly as comprising a conventional electric motor 13couplied to a power distribution box 14 from which the shafts 11 and l2of the shut-ter discs and a driving spindle l5 for a film sprocketroller lo are driven. The connection between driving shaft IJS androller lo is establishedby a conical gear ll7.

Between the film speed and the differential speed of the shutter discs`on one hand, Aand the :shutter speed on the other hand, a constantratio may be maintained in general. lf it is supposed that, by a changein flying speed v or altitude h, or both, the speed (v/lz)f (where f isthe focal length of the camera) of the image in the focal plane ismultiplied by a factor k l, the film speed and the repetition frequencymust be multiplied by the same facto-r k, if the overlapping factor andthe interspaces between successive pictures or exposures are to remainequal.

Consequently, the difference in speed between the image and the film ismultiplied by the factor k as well. It is evident that, in order toavoid an increase of the resultant blurring, the exposure time maypreferably be divided by the factor k, which means that the rotationalspeed of `which 35 is driven by the driving mechanism.

i disc ll should be multiplied by the same factor k as the film `speedand the repetition frequency.

In this wa the construction of the driving mechanism can be very simpledue to the fact that all driven parts may have a fixed mechanicalcoupling to this mechanism and there is no need that they be controlledindividually. The control of the camera will consist merely in varying,by any conventional means, the speed of electric motor d3 proportionallyto `the quotient of the flying speed v and the flying altitude lz.Moreover, there is no need for a very precise measurement of the actualvalue of this quotient, as in the case of conventional cameras havingimage motion control, due to the fact that the extremely short exposuresprevent :the additional blurring caused by a possible inaccuracy.

lt may be observed that in case a fixed relation exists between thevarious speeds concerned, the adaptation of the camera to the prevailinglight conditions must be effected by the aid of the lens stop. Thus, theshortest exposure time is so chosen that under comparatively unfavorablelight conditions on the envisaged type of film reasonable pictures canbe made when the lens is at maximum aperture. Thereby, for given maximumimage speed and overlapping factor, the blurring resulting from imageyand film speed is determined. With decreasing v/h-ratio the shutter andfilm speed are decreased proportionally to the image speed `whereby theoverlapping factor and the blurring remain constant. The lens is stoppeddown at the same time in order to correct for the increased exposuretime. v

Film i3 in FiGS. 2 and 3 is advanced longitudinally from the supplyspool 9 over a guiding roller 19 towards the image area. Here, the filmis drawn between a planeparallel glass plate 2li and a back plate 2lspaced from the glass plate 2@ a distance such that the film at allpoints of the image area is within the depth of field of the lens. Thefilm is transported over -a guiding roller 22 by a sprocket roller locooperating with counter roller 23 and taken up at the take-up spoolitl.

As shown diagrammatically in FlG. 2, the lens system 7' is provided witha shutter 2dof any `known type by which means a series of successiveexposures may be started and closed.

This shutter may beA opened when the driving mechanism and the elementscoupled thereto have attained the required speed and may be closed againas soon as sufficient exposures have been made. It will readily beunderstood that the function of a between-the-lens shutter such as 24may alternatively be performed by an element which, in addition to thepair of shutter discs, is mounted in front of the focal plane and can beshifted, rotated or moved `otherwise out of the light beam during aseries of exposures.

In FIGS. 4 and 5 a twin camera which may be used as :astereo-photographic camera is schematically shown as comprising arectangular flat box 56 in which the shutter discs 25 and 2o areaccommodated. A pair of lens tubes are mounted on one side of the box 5oof which only one, designated 5'?, is visible in the drawing, and acover 53 forms a part of the camera body under which the film spools,the Idriving mechanism and other related apparatus not essential for thepresent invention are mounted. As seen in FG. 5, this cover 553? `formsa cornpartment 2? for the driving mechanism and comprises .two easilydetachable lids for the film compartments. One ofA the lids has beenremoved in F'G. 5 and the other is designated 26. The film 3T. is drawnfrom a supply spool Z9 to a take-up spool 3@ by sprocket rollers 34 and35, of It being understood that FIG. 5 is an exploded perspective View.Supporting shafts 32 and 33, for spools 29' and 39 respectively, proiectfrom a side wall of the camera body compartment in which the drivingmechanism is housed. The driving force is supplied by an electric motorof conventional `design but preferably having a variable speed. Gn theshaft of this motor a pair Vof sprocket wheels (only one of lwhich,designated `41, is visible in the drawing) are mounted. These sprocke-twheels cooperate with toothed bolts 42 and 43, driving a pair ofsprocket wheels mounted on the coaxial shafts 38, 39 of discs 2.5, 26,respectively. The diameters of :the sprocket wheels are slightlydifferent to insure that the rotational speeds of the discs -have therequired `relation to each other, as described hereinbefore inconnection with FIG. 1.

On shaft 38 another sprocket wheel 44 is provided which, by means of iatoothed belt 4d drives a sprocket Wheel 46. The latter Wheel isconnected through an electromagnetic coupling mechanism 47 to a worm 48which drives a worm gear 49 on a shaft 50 having ball bearings 51 and52. The end portions of this shaft 50; such as 35, form ilm drivingsprockets, extending into the film compartments of the camera. In FlG. 4of the drawing there is further illustrated for one half of the camera asimple means for driving the spindle .33 of take-up spool 3l),consisting in wheels 53 and 54 on a shaft 49' and spindle 33,respectively, which are connected in driving relation by a crossed belt5'5.

As is usual in apparatus of the type concerned this arrangement shouldhold the film tightly drawn between the feed sprocket rollers and thetake-up spool and, to this end, the belt may easily slip with respect toeither of the wheels 53 and 54. It will be understood that a second lmstrip (not shown) is mounted in compartment 2S and is advanced similarlyto lm strip 31.

The camera illustrated in FIGS. 4 and 5 is particularly adaptcdto makeseries of stereometric pictures from an aeroplane in a mannerverysimilar to that described in connection with the camera of FIGS. 2and 3. Thus, as a first possibility, motor 4() drives the discs 25 and26 at predetermined speeds having a ratio such that the apertures inboth discs :are in correspondence with each other during one passageacross the image area 36- of one of the objectives, an-d, after a numberof revolutions appear at the same time before the field image 37 of theother objective. Assuming for instance that the discs run at 5500 and6500 revolutions/min. it takes tive and a half revolutions of the slowerdisc to have the apertures in correspondence before the opposed fieldimage or image area and another five and a half revolutions to come intoconjunction again in -front of the first image area. After theelectromagnetic coupling 47 has been actuated, by circuitry no-t shown,the --lms are drawn at constant speed through the focal planes.

Preferably, the motor 40 and the discs 25 and Z6 will be rotatablydriven during the whole flight and the electromagnetic coupling 47 willbe switched on each time a series of exposures is to be made. At thesame time as the coupling` 47 is actua-ted a pair of between-the-lensshutters, not shown, in the camera objectives may be actuated so as toprevent incident light from entering the camera through the apertures inrotating discs Z5 and 26 as long as no exposures are to be made. It willbe understood that with coupling 47 energized overlapping pictures areobtained on bo-th film strips whose stereoscopic base is equal to thedistance flown by the aeroplane dur ing iive and a half revolutions ofthe slower disc.

Alternatively, however, the arrangement may be such that both of theimage areas are swept by the apertures during one and the samerevolution. Assuming, as in connection with FIG. l, that 4the discs runat speed of 8100 and 9000 revolutions/ min. the widest aperture mustcover `an angle of about 40, with an exposure aperture of 3, in order toinsure that the latter aperture is fully open during the time it passesbefore the image areas of both objectives and therebetween, whereas itis obstructed again by the second disc at the time it reaches the firstimage area during the next revolution. lt is to be understood that, ascorresponding pictures on both film strips are 4made during one and thesame revolution of the disc, the stereoscopic base will be much smallerin this case than in the case explained above.

As illustrated in FIG. 6y it is also possible to construct the discssuch that the corresponding exposures on both films are made exactly atthe same time by each of the discs. Instead of only one aperture eachdiscs has a pair of identical apertures radially opposite to each other.In FIG. 6 the parts having their equivalents in FIG. l are indicated byidentical reference numerals and the additional parts are designated byprimed reference numerals. If it is assumed that the disc 1 runs at90'00 `and the other, 4, at 8500 reVs./min., the apertures 5 and S inthe slower disc will be in correspondence with each of the apertures 2and 2 respectively in the other disc 500 times per minute so that thetotal number of exposures made on both films will amount to 1000 perminute. It will be understood that in this case the stereoscopic base isreduced to the distance between the two lenses of the camera.

In the perspective view of FIG. 7 an alternative iilm drivingarrangement is shown, for use in a camera of the type illustrated inFIGS. l4 and 5. According to` FIG. 7 the films may be drivenindependently. Thus, for each of the film driving sprockets individual:sets of worms 59 and 60 and worm wheels 61 and 62 are provided insteadof the single worm and worm wheel arrangement 48, 49 of FIG. 4. TheWorms '59 and 6l) in FIG. 7 are mounted on shafts which, throughindividual electromagnetic couplings 63 and 64, sprocket wheels 65 and66 and toothed belts 66 and 67 derive rotational force from individualsprocket wheels on shaft 38. Accordingly, one may load identical filmsin the camera and make stereoscopic pictures as described above bydriving both films at the same time. Alternatively, lidentical films maybe exposed one after the other by energizing couplings 63 and 64alternatively. It is also possible, however, to have different films(f.i. iilms of different sensitivity or blackand-white and color lm)placed in the camera of which alternative use is made.,

It may be indicated here that, of course, for making stereoscopicpictures it is not indispensable to use a twolens camera. With theone-lens camera described above, however, it is preferable to reduce theoverlapping portions of successive pictures as much as possible in orderto minimize the differential speed between the film and the image andthe resulting blurring. On the other hand, of course, only overlappingportions of successive pictures made by a onelens camera can be viewedstereoscopically. It is preferred, therefore, if stereoscopic work isaimed at, to use a twin camera as illustrated in FIGS. 4 to 7.

A miniature camera shown in FIGS. 8 and 9 is illustrative of the factthat the focal plane shutter according to -of which the latter isdetachable for the purpose of film loading. The interior of the camerais divided in two compartments by a partition or wall 7i). The uppercompartment houses the film supply and take-up spools 71 and 72,respectively, a film guiding roller 73 and a sprocket roller 74. Mountedon the front wall 75 of the housing is a lens tube 76. The lowercompartment houses the spring motor and the gearing mechanism be,- tweenthis motor and the shutter disc shafts. The shutter discs 77 and 78 areconfined in a separate compartment between the front Wall 75 of thecamera and a partition 79. Windows Si) and 81 in these walls allow thelight rays to pass towards the focal plane of the camera. A View finder82 of conventional design is placed on top of the portion 6d of thecamera housing.

The spring motor comprises a springV drum 83 rotatably mounted on awind-up shaft 84 and having an inner rim 85 to which one endof thecoiled spring 87 is atatrasos tac'ncd and an outer rim 36 which isprovided with circumferential toothing. The other end of tie spring isattached to the wind-up shaft. Between a rear wall 88 of the housing anda supporting partition S9 a ratchet il and pawl '9i-arc provided so asto prevent the spring S7 from turning shaft 84 bach when it is wound upby means of the knob @E on shaft Drum 83 further carries a pin 9.3which, in cooperation with spring-loaded pawl 94 retains drum 33 in theposition shown in PEG. 7 when the camera is in a rest position or whenthe spring S7 is wound up. A nose portion 95' on pawi is in engagementwith a hook portion 36 on a spring-loaded lever $7 which is pivotallyconnected at @8 to a longitudinally slidable member 99. This, in turn,is dctachably connected to a shaft iti@ of a push button lili which in arest position is held in an upward position by a spring MEZ.

The toothed outer rim iid of drum S3 engages a gear 1&3 fixed on shaftfue which further carries two gears i195 and of slightly differentdiameter, which cooperate with two gears lil? and itis mounted on thecoaxial shafts lili? and il@ of the shutter discs '77 and '73respectively. The gear ratio of the pair of gears ltiS and lti is higherthan that of the gears M6 and ilfi in accordance with the principle ofthe invention as outlined hereinbebefore.

The camera is operated in a manner not rnuch different from that ofconventional roll film cameras. In the inoperative position of thecamera the position of the shutter discs 77, 73, as determined by thestop pin 93, is such, that incident light is shut ofic from the film.The apertures in the disc are spaced apart by a considerable angle so asto insure that only after a number of revolutions of the shutter discsthey will be in correspondence before the image arca. The film isreadied for exposure and positioned in correspondence with the imagearea by rotating knob fill fixed to the sprocket roller 74 cooperativewith the taire-up spool 72 whose spindle is coupled to relier 7d bymeans of a belt lf2. Then, the spring 87 is wound up by rotating a knob@2, fixed to the shaft 8d, clock-wise until the desired force isattained. By varying the tension of spring 37 it is possible to vary theeffective exposure time of the shutter.

When an exposure is to be made the push button lill is pressed wherebythe hook portion 96 on lever 97 rotates pawl 9d clock-wise. Consequentlypawl 94 slips off of stop pin 93 and the spring 87 forces drum $3 torotate clock-wise. When stop pin 93 passes the lower part of lever 97 itpushes the latter to the right whereupon portion 96 of the lever losesContact with nose 95 of pawl 9d and ythe pawi is free to return to theposition shown. Thus, when drum 33 has rnade one revolution it is againstopped the pawl 9d engaging pin 93. The gear ratio between drum S3 andthe shafts N9, ll@ of the shutter discs is such that the latter by thattime have made 11 and lib revolutions respectively. Assuming that theexposure aperture in the rest position was before the image area and theother aperture was in the position opposite thereto the apertures willbe in correspondence before the image surface after five and a halfrevolutions of the exposure apertures and the exposure takes place. Ofcourse, there is a certain time delay between the actuation of pushbutton Mil and the actual exposure. Due to the high speed of the discsthis delay is very small, however7 and does not give rise todifliculties in operating the camera. The remaining revolutions of thediscs serve to restore the initial position of the slu tter discs. Toprepare the camera for the next exposure the film has to be conveyed onestep and the shutter spring 87' must be re- Wound.

Finally, in the arrangement of FIG. l it is easy to dev monstrate thatby adding to a focal plane shutter as described in connection with FIG.l a third disc the repetition frequency of the shutter can be reduced toany value which may be desired. The three discs are designated 1, 4 andlli and have apertures 2, 5 and 113 respectively.

The discs are mounted on coaxial shafts and are rotatably driven bysuitable mechanism, not shown, at speeds of 8100 and 8250 revs./min.respectively. As discussed in connection with PEG. 1 aperture 5 will bepassed by aperture Z each tenth revolution of disc ll. However, in thearrangement of FIG. l0 only every sixth of these occurrences will resultin an exposure due to the fact that aperture il@ is passed by aperture 2every twelfth revolution. Hence, it will take sixty revolutions of disc1 before correspondence of the three apertures is repeated and therepetition frequency will amount to exposures per minute. The apertureM5 may cover an angle of about 10.5 in view of the slightly higher speedof disc M2, if compared with disc 4.

lt will be apparent from the foregoing that many other arrangements,including such having four or even more shutter discs, may be designedto suit any requirements regarding shutter speed and number ofexposures. Moreover, it is within the scope of this invention to impartan intermi, ent rotation to a disc like 112 so that it may act as anindependent shutter element for starting and closing the operation ofthe focal plane shutter proper.

While preferred embodiments of the invention have been illustrated anddescribed, it will be understood that the invention is in no way limitedto these embodiments and that many changes may be made within the spiritand scope of the invention as defined by the following claims.

What we claim and desire to secure by Letters Patent is:

l. In an aerial camera for automatically taking a series of overlappingpictures from a flying airplane in rapid sequence on a driven roll film,in combination, an objective, means deningv an exposure gate in thefocal plane of said objective, a film drive mechanism to continuouslyadvance the film in said focal plane, in operation, in the direction theimage travels and across said exposure gate at a constant rate duringand between successive exposures, means for adjusting the speed ofmovement of the roll film across said exposure gate so that it exceedsthe speed of movement of the image due to the relative speed of the yingairplane and the terrain being photographed by a percentage at leastequal to the percentage of overlap of said photographs therebycontinuously overcomensating for image motion, and a focal plane shutterfor periodically exposing the film in said focal plane at intervais atleast equal to the time required for the film to traverse said exposuregate at said constant speed, said focal plane shutter comprising a pairof coaxial, axially spaced, adjacent, light-impervious, circular discsrotatably driven in parallel planes about a common axis extendingperpendicular to said focal plane, said discs being disposed a shortdistance in front of said focal plane and each having a peripheralaperture extending radially inwardly to effectively expose the fullheight of said exposure gate when driven past said gate, the aperture inone of said discs diverging linearly toward the periphery of said onedisc and being substantially narrower than the aperture in the otherdisc, means for rotatably driving the two discs in a common direction atdifferent speeds having a fixed ratio to each other to periodically movesaid apertures concurrently past said exposure gate to cause periodicexposures of said film separated by time intervals during which each ofthe discs makes more than one revolution and an effective exposure timehaving a duration for each point in said exposure gate effective tolimit the unsharpness caused by 'the overcompensation of said irnagemotion.

2. ln an aerial camera for automatically taking a series of overlappingpictures from a fiying airplane in rapid sequence on a driven roll film,in combination, an objective, means defining an exposure gate in thefocal plane of said objective, a film drive mechanism to advance thefilm, in operation, continuously in the direction the image travels andacross said exposure gate at a constant rate during and betweensuccessive exposures, means for adjusting the speed of movement of theroll film across said exposure gate so that it exceeds the speed ofmovement of the imago due to the relative speed of the iiying airplaneand the terrain being photographed by a percentage at least equal to thepercentage of overlap of said photographs thereby continuouslyovercompensating for image motion, and a focal plane shutter forperiodically exposing the film in said focal plane at intervals at leastegual to the time required for the film to traverse said exposure gateat said constant speed, said focal plane shutter comprising meanseiiective in operation to cause said exposure time to have a durationfor each point in said exposure gate eiective to limit the unsharpnesscaused by the overcompensation of said image motion.

3. ln an aerial camera for automatically taking rapid sequences ofoverlapping photographs from a flying airplane on a driven roll nlm, incombination, an objective, means deiining an exposure gate in the focalplane of said objective, a focal plane shutter comprising a pair ofcoaxial, axially spaced, adjacent, light-impervious, circular discsrotatably driven in parallel planes about a common axis extendingperpendicular to the focal plane, said discs being disposed a shortdistance in front of the focal. plane and each having a peripheralaperture extending radially inwardly to ellectively expose the fullheight of the exposure gate when driven past said gate, the aperture inone of the discs diverging linearly toward the periphery of the disc andbeing substantially narrower than the aperture in the other disc, meansfor rotatably driving the two discs in a common direction at differentspeeds having a iixed ratio to each other to periodically move saidapertures concurrently past said exposure gate to cause periodicexposures of said lilrn separated by time intervals during whichreach ofthe discs maires more than one revolution, means cooperative with saidshutter driving means to advance, in operation, continuously said rollfilm past said exposure gate at a constant speed having a ixed ratio tothe rotational speeds of said shutter discs to thereby cause said rollilm to travel during said intervals a iixed distance at least equal tothe width of the exposure gate in the direction of film travel, saidfilm advancing means comprising means Vfor adjusting the speed or"movement of said film across said exposure gate so that it exceeds thespeed of movement of the image due to the relative speed of a flyingairplane and the terrain being photographed by a percentage at leastequal to the percentage of overlap of said photographs therebycontinuously overcompensating for image motion, and the effectiveexposure time of said focal plane shutter for each point of exposure orsaid film in the focal plane being less than 1% of said intervalsbetween subsequent exposures to effectively limit the unsharpncss causedby the overcompensation for said image motion.

4. ln a photographic camera, in combination, two objectives havingparallel optical axes and a common focal plane, an exposure gate foreach of said objectives in saidfocal piane, a focal plane shuttercooperative with each of said exposure gates and comprising a pair ofcoaxial, axially spaced, adjacent, light-impervious, circular, discsrotatably driven in parallel planes about a common axis extendingperpendicular to the focal plane and between said objective axes, eachdisc having a peripheral aperture extending radially inwardlysul'liciently to expose the full height of each of the exposure gates,one of the apertures diverging linearly in a direction towards theperiphery of its disc and being narrower than the other, means forrotatably driving the two discs in a common direction at differentspeeds having apredeterniined ratio to each other so that said aperturesmove in conjunction alternately past each of said exposure gates attimes separated by intervals of equal duration during which each of saiddiscs maires n+1/2 revolutions and n eing a diterent number for the twodiscs.

References Cited in the tile of this patent UNITED STATES PATENTS FranceMar. 10, 1921

1. IN AN AERIAL CAMERA FOR AUTOMATICALLY TAKING A SERIES OF OVERLAPPINGPICTURES FROM A FLYING AIRPLANE IN RAPID SEQUENCE ON A DRIVEN ROLL FILM,IN COMBINATION, AN OBJECTIVE, MEANS DEFINING AN EXPOSURE GATE IN THEFOCAL PLANE OF SAID OBJECTIVE, A FILM DRIVE MECHANISM TO CONTINUOUSLYADVANCE THE FILM IN SAID FOCAL PLANE, IN OPERATION, IN THE DIRECTION THEIMAGE TRAVELS AND ACROSS SAID EXPOSURE GATE AT A CONSTANT RATE DURINGAND BETWEEN SUCCESSIVE EXPOSURES; MEANS FOR ADJUSTING THE SPEED OFMOVEMENT OF THE ROLL FILM ACROSS SAID EXPOSURE GATE SO THAT IT EXCEEDSTHE SPEED OF MOVEMENT OF THE IMAGE DUE TO THE RELATIVE SPEED OF THEFLYING AIRPLANE AND THE TERRAIN BEING PHOTOGRAPHED BY A PERCENTAGE ATLEAST EQUAL TO THE PERCENTAGE OF OVERLAP OF SAID PHOTOGRAPHS THEREBYCONTINUOUSLY OVERCOMPENSATING FOR IMAGE MOTION, AND A FOCAL PLANESHUTTER FOR PERIODICALLY EXPOSING THE FILM IN SAID FOCAL PLANE ATINTERVALS AT LEAST EQUAL TO THE TIME REQUIRED FOR THE FILM TO TRAVERSESAID EXPOSURE GATE AT SAID CONSTANT SPEED, SAID FOCAL PLANE SHUTTERCOMPRISING A PAIR OF COAXIAL, AXIALLY SPACED, ADJACENT,LIGHT-IMPERVIOUS, CIRCULAR DISCS ROTATABLY DRIVEN IN PARALLEL PLANESABOUT A COMMON AXIS EXTENDING PERPENDICULAR TO SAID FOCAL PLANE, SAIDDISCS BEING DISPOSED A SHORT DISTANCE IN FRONT OF SAID FOCAL PLANE ANDEACH HAVING A PERIPHERAL APERTURE EXTENDING RADIALLY INWARDLY TOEFFECTIVELY EXPOSE THE FULL HEIGHT OF SAID EXPOSURE GATE WHEN DRIVENPAST SAID GATE, THE APERTURE IN ONE OF SAID DISCS DIVERGING LINEARLYTOWARD THE PERIPHERY OF SAID ONE DISC AND BEING SUBSTANTIALLY NARROWERTHAN THE APERTURE IN THE OTHER DISC, MEANS FOR ROTATABLY DRIVING THE TWODISCS IN A COMMON DIRECTION AT DIFFERENT SPEEDS HAVING A FIXED RATIO TOEACH OTHER TO PERIODICALLY MOVE SAID APERTURES CONCURRENTLY PAST SAIDEXPOSURE GATE TO CAUSE PERIODIC EXPOSURES OF SAID FILM SEPARATED BY TIMEINTERVALS DURING WHICH EACH OF THE DISCS MAKES MORE THAN ONE REVOLUTIONAND AN EFFECTIVE EXPOSURE TIME HAVING A DURATION FOR EACH POINT IN SAIDEXPOSURE GATE EFFECTIVE TO LIMIT THE UNSHARPNESS CAUSED BY THEOVERCOMPENSATION OF SAID IMAGE MOTION.